Method and apparatus for alleviating scouring about legs of a marine structure



METHOD AND APPARATUS FOR ALLEVIATING SCOURING ABOUT LEGS OF A MARINESTRUCTURE July 8, 1969 A c. MITCHELL. JR 3,453,830

Filed March 13, 1968 Sheet I of 2 INVEN'TOR ALBERT C. MITCHELL, JR.

mdz%m ATTORNEY A.,C. MITCHELL. JR METHOD AND APPARAT Filed March 13,1968 July 8, 1969 7 3,453,830 US FOR ALLEVIA'I'ING SCOUHING ABOUT LEGSOF A MARINE STRUCTURE Sheet FIG. 2

FIG. 3

INVENTOR ALBERT C. MITCHELL, JR.

ATTORNEY United States Patent US. 'Cl. 61--46.5 11 Claims ABSTRACT OFTHE DISCLOSURE A method and apparatus for placing antiscouring materialsor objects about the lower end of an extendible leg of a marinestructure to alleviate scouring wherein said lower end of said leg ispositioned on the bottom of a body of water and the upper end supports awork platform. The invention includes at least one pallet attached tothe leg. An extendible means such as a net is attached to each pallet;the net normally lying flat on the pallet when unextended and having apyramidal configuration when extended. The antiscouring material orobjects are piled on the net while it is in a flattened condition andprior to the positioning of the leg on the bottom. The net is extendedby a cable after the leg is positioned to force the antiscouringmaterial or objects off the pallet to place the objects around the leg.

Background of the invention This invention relates to a method andapparatus for alleviating scouring about the legs of a marine structureand, more particularly, relates to a method and apparatus for placingantiscouring materials or objects about the legs of said structure.

The drilling of underwater wells in search of oil or other minerals isnow commonplace. In carrying out such drilling operations, differenttypes of marine structures are used depending primarily upon the depthof water encountered. One of the most common of these structures is onewhich is used in depths of water between 40 and 300 feet and is commonlyreferred to in the art as a jack-up rig.

A typical jack-up rig is comprised of a floating barge or work platformon which is carried the drilling derrick, drawworks, mud tanks andpumps, and the other associated equipment necessary for the actualdrilling of an underwater well. Spaced about the periphery of theplatform and extending through openings or guides therein are aplurality of skeletal legs. These legs are normally retracted andsupported in a position above the platform whenever the rig is floatedfrom one location to another. Once the rig has been positioned over thedesired drilling site each leg is lowered through its respectiveplatform opening or guide until it engages the bottom of the water whereit partially embeds itself in the soil. In some instances, a spud canmay be provided at the lower end of each leg to aid in embedding thelegs in the bottom. When each leg is in its desired position on thebottom, jacks on the rig are actuated to lift the platform out of thewater and onto the legs. By being supported above the surface of thewater on legs which are effectively anchored to the bottom of the water,the platform normally provides a stable base for drilling operations.

Unfortunately, however, in some bodies of water the platform does notremain stable due to the scouring of soil from around the embeddedportions of the legs. This scouring, which is believed to be caused bytides, waves, and/or strong underwater currents, may shift or move largevolumes of sand, gravel, or other material from around the legs inrelatively short periods of time. This 3,453,830 Patented July 8, 1969undermining of the legs allows one or more of said legs to shift or sinkfurther into the bottom thereby causing the platform to tilt or shiftwhich in turn may snap drilling lines, dislodge valuable equipment, ordestroy the platform itself. In view of this, it is obvious that theproblem of scouring is one which must be: considered when jack-up rigsor like structures are used in underwater operations.

In the past, various approaches have been taken to prevent scouring ofsoil from around the legs of such structures. These approaches haveincluded, for example, 1) using rigid barriers around the legs such assteel pilings or scouring skirts; (2) consolidating the soil around thelegs by use of hardening resins, concrete, Or other soil solidifyingmaterial; and (3) surrounding the exposed areas of the legs on thebottom with piles of unconsolidated, insoluble material or objects, suchas large size gravel, concrete blocks, anchored willow mats, ofsandbags.

Of these approaches, the latter one of using piles of unconsolidatedmaterial or objects to surround the lower ends of the legs is one of themost commonly used. This antiscouring material or objects beingunconsolidated have a tendency to fall into any undermining orexcavations caused by scouring, thereby maintaining a relatively firmfoundation around the legs and preventing any serious shift of the legs.Also, by using unconsolidated material or objects instead of materialwhich solidifies around the legs, the rig can be moved more easily atthe completion of drilling operations.

It has been found that larger, unconsolidated, antiscouring objects,such as concrete blocks and preferably sandbags, will resist scouringbetter than smaller material (e.g., gravel) since due to their weightthey cannot be moved as easily from around the legs by scouring actionof underwater currents. However, in the past due to the bulk of theseobjects, considerable time was required to lower and place them in theirproper positions. Also since this placement involved the efforts ofunderwater divers for relatively long periods, it has been a relativelyexpensive procedure to follow.

Summary of the invention In accordance with the present invention, thereis provided a new and improved method and apparatus for the placement oflarge, unconsolidated, antiscouring materials or objects such assandbags or the like about the legs of an underwater drilling structureto alleviate the scouring of soil from about said legs. In carrying outthe present invention, one or more pallets are fixedly secured on eachleg of the platform. Each of these pallets is provided with a flexible,extendible means which is preferably a specially shaped net or the like.The net which lies flat on the pallet when in an unextended or collapsedposition has a pyramidal configurationwhen raised or pulled to anextended position, said pyramidal configuration having a base whichsubstantially conforms to the periphery of the pallet and which isattached thereto. A cable or rope is attached to the apex of thepyramidal net and is operable from the platform when the structure is inposition. The antiscouring materials or objects to be placed about thelegs are piled onto the flattened net prior to the legs being finallypositioned in the water. When the legs are in position, the net ispulled to an extended position by the cable attached to the net. As thenet is extended it forces the antiscouring materials or objects ofl thesides of the pallet so that they fall downward around the correspondingsides of the leg. As is obvious from the above, the invention provides aquick and efilcient means of placing antiscouring objects about the legsof an underwater drilling structure which requires neither the timeinterval nor the extensive efforts of underwater divers previouslyrequired in other placement procedures. If desired, a diver can beemployed to check the final placement of the objects and slightlyreposition some of of them, if necessary; but the time required will beonly a fraction of that previously needed.

The actual construction, operation, and the apparent advantages of theinvention will be better understood by referring to the drawings inwhich like numerals identify like parts and in which:

Brief description of the drawings FIGURE 1 is a perspective view, partlybroken away, of an underwater drilling structure employing the presentinvention;

FIGURE 2 is a perspective illustration of the present invention; and

FIGURE 3 is a perspective view taken along lines 33 of FIGURE 2 with theinvention in an extended position.

Description of the preferred embodiments Referring more particularly toFIGURE 1, an underwater drilling structure is shown in operationalposition in a body of water 11. The drilling structure shown in thefigure belongs to the class of marine structures commonly known asjack-up rigs and this type of rig is widely used in underwater drillingoperations. The structure 10 is comprised of a fioatable barge or workplatform 12 having a plurality of extendible, skeletal legs 13 spacedabout the periphery thereof. Structure 10 is shown as having four legs13, but it should be recognized that some rigs may have only three whileothers may have more than four. In any case, the number of legs does notaffect the present invention. Drilling derrick 14, work cranes 15, andother necessary drilling equipment are mounted on platform 12 as is wellknown in the art. Legs 13 extend through guide members 16 which aremounted on or form part of the platform 12. Legs 13 are normallyretracted (not shown) and extend above platform 12 whenever thestructure is floated to or from a drilling location. Legs 13 arepreferably comprised of a plurality of tubular members 20 connectedtogether by cross members 21 to form a polygon cross-sectionalconfiguration. Legs 13 are illustrated as having three tubular members20 which give legs 13 a triangular cross section, but more than threemembers 20 could be used if desired. Additional vertical braces 22 arenormally used to strengthen the legs as is well known in the art. Spudcan 23 is provided at the lower end of each leg to improve thepenetration ability of each leg and also to aid in removal of the legswhen drilling operations are completed. Use of spud cans for thispurpose is well known.

In accordance with the present invention, at least one pallet 25 isprovided on each leg 13 of the drilling structure 10. Referring moreparticularly to FIGURES 2 and 3, pallet 25 is comprised of a pluralityof brace members 26 joined together to form a base having substantiallythe same configuration as that of the cross section of skeletal legs 13;e.g., in the present illustration the base will be triangularly shaped.The base is secured to cross members 21 at the desired level of legs 13by means of a plurality of clamp means 27. The triangular base iscompletely covered by heavy bridge timbers 28 or the like which aresecured thereto to form a solid foundation for pallet 25. A flexible,extendible means 29 is provided for each pallet 25. This means 29 ispreferably comprised of a heavy netlike material formed from nlyon orwire but can also be comprised of solid materials such as heavy cloth orcanvas, reinforced plastic material, or any other similar material.Means 29 or net 29, as it will hereinafter be referred to, isconstructed so that it will form a pyramidal configuration when it is inits extended position. The base 29a (FIGURE 3) of the pyramidalconfiguration substantially conforms to the configuration and dimensionsof pallet 25 and is secured to the periphery of pallet 25 by bradding,bolting, gluing, or any other means well known in the art. In thepresent instant, the

base of net 29 is a triangle but if leg 13 were comprised of fourtubular members instead of three, the base would be rectangular and soon. A rope or cable 30 is secured to the apex 29b of net 29 by means ofa hook and eye (not shown) or similar means and extends upward toplatform 12 for a purpose explained below.

Net 29, being flexible, will be fiat on pallet 25 when in an unextendedor collapsed position. The antiscouring material or objects, e.g.,sandbags 31, to be placed about legs 13 are then piled or loaded ontonet 29 while it is in the flattened condition.

Operation of the present invention is as follows: Skeletal legs 13 of astandard-type, jack-up marine structure 10 are equipped with pallets 25as explained above. As is well known in the art, leg 13 will beretracted and will extend upward from platform 12 while structure 10 isfloated into position over a desired drilling site. Prior to or uponreaching the proposed site, sandbags 31 or other desired antiscouringmaterial is loaded onto pallet 25 and hence flattened net 29. Legs 13are then lowered until spud cans 23 engage the bottom 17. Spud cans 23can be used to wash-in the lower portions of leg 13 if the soil isotherwise too hard to allow legs 13 to become partially embeddedtherein. When legs 13 are positioned on bottom 17, jacking units (notshown) cooperate with legs 13 to lift platform 12 out of the water to aposition above the surface thereof where it is supported entirely onlegs 13.

Next, cable 30 is pulled upward by means of a Winch (not shown) or thelike to raise net 29 to an extended position. As net 29 is extended toits pyramidal configuration, it forces sandbags 31 off each of the sidesof pallet 25 so that sandbags 31 will fall downward around spud can 23as shown in FIGURE 1. Due to the weight of sandbags 31 and therelatively short distance which they travel, most of the sandbags willassume a proper position about spud cans 23. If desired, a single divercan inspect the actual position of the sandbags and reposition some ofthem, if necessary.

Although a particular embodiment of the subject invention has beenillustrated and described, the disclosure is intended to cover allchanges and modifications therein which do not constitute departure fromthe spirit and scope of the invention. For example, the presentinvention has been described in conjunction with a drilling rig but itshould be recognized that it would work equally as well with othersimilar marine structures such as workover rigs or the like. Also,although only one pallet is shown on each leg, several pallets could beprovided by securing them, one above the other, to respective crossmembers 21 and then diverting individual cables from each associated net29 by means of pulleys so that the cables would run up the sides oftubular members 20 to platform 12.

What is claimed is:

1. In a marine structure of the type comprising a floatable platformhaving a plurality of extendible, skeletal legs having a polygonal crosssection which are normally retracted to a position above the platformwhen said structure is being moved on a body of water and which engagethe bottom of said water when said legs are extended, means forpositioning material or objects about the lower ends of said legs toprevent scouring comprising:

at least one pallet having substantially the same canfiguration as saidpolygonal cross section of said skeletal legs secured to each of saidlegs at a point which will lie below the surface of said water when saidleg is extended,

an extendible means which, when extended, has a pyramidal configurationhaving base dimensions conforming to the periphery of said pallet, saidextendible means being attached to said periphery of said pallet andnormally lying fiat on said pallet when in an unextended or collapsedposition, said means being adapted to receive said material or objectsto be positioned while said means is flat on said pallet; and

means connected to said extendible means and operable from said platformto extend said extendible means to an extended position when saidskeletal legs engage the bottom of said water.

2. The structure of claim 1 wherein:

said means to extend said extendible means includes a cable connected tosaid extendible means and extending to said platform.

3. The structure of claim 2 wherein:

said extendible means is comprised of netlike material.

4. The structure of claim 1 wherein:

said marine structure is a jack-up structure.

5. In a marine structure comprising a platform having extendible legmeans thereon which is normally retracted to a position above theplatform during movement of said structure and which engages the bottomof a body of water when in an extended position, means for placingmaterial or objects about the lower end of said leg means to preventscouring:

support means on said leg means adapted to receive and support saidmaterial or objects prior to said leg means being extended, said supportmeans being positioned on said leg means so that it will lie below thesurface of the water when said leg means is extended; and

means on said support means to displace said material or objects fromsaid support means when said leg means is extended.

6. The structure of claim 5 wherein:

said support means is a pallet.

7. The structure of claim 6 wherein said means to displace said materialor objects includes:

an extendible means which, when extended, has a pyramidal configurationattached to said pallet, said extendible means normally lying flat onsaid pallet when in an unextended or collapsed position, said extendiblemeans adapted to receive said material or objects to be positioned whilesaid means is flat on said pallet; and

means connected to said extendible means and operable from said platformto extend said extendible means to an extended position.

8. The structure of claim 7 wherein: said means to extend saidextendible means includes a cable connected to said extendible means andextending to said platform. 9. The structure of claim 8 wherein: saidextendible means is comprised of netlike material. 10. A method ofpositioning antiscouring material or objects about the lower end of aleg of a marine structure to alleviate scouring around said leg whereinsaid lower end of said leg is positioned on the bottom of a body ofwater and the upper end of said leg supports a work platform or thelike, the method comprising:

securing at least one pallet to said leg at a position on said leg sothat said pallet will be below the surface of the water when said lowerend of said leg is positioned on the bottom of said body of water;attaching a flexible means having a pyramidal configuration when in anextended position to said pallet, said flexible means lyingsubstantially flat on said pallet when not in an extended position;placing said antiscouring material or objects on said flexible meanswhile said flexible means is in a flattened position on said palletprior to the positioning of said leg in said body of water; andextending said flexible means to said extended position after said legis positioned on the bottom of said body of water whereby saidantiscouring material or objects are displaced by said flexible meansfrom said pallet to fall to a position about the lower end of said leg.11. The method of claim 10 wherein: said antiscouring materials orobjects are sandbags.

References Cited UNITED STATES PATENTS 2,940,266 6/1960 Smith 61--46.53,312,069 4/1967 Jorda 61-1 X 3,394,553 7/1968 Vidal 61-46.5

JACOB SHAPIRO, Primary Examiner.

U.S. Cl. X.R. 6l-50, 52

